VISUAL AND AUDITORY DISTINCTIONS 173-
Quite different in external appearance, three sets of blocks
repeat the graduation in one, two and three dimensions.
We have here large pieces of wood painted in bright colours,
in three systems which we call — the system of rods and lengths,
the system of prisms, the system of cubes.
The rods, having the same square section of 2 cms. sides, are
painted red, differ from each other by 10 cms. the longest of the
series being a metre long; from that the rods decrease by one
decimetre at a time.
The manipulation of such long, cumbrous objects demands
from the child movement of the whole body. He has to go back
and forth to transport these rods and then he has to place them
side by side in the order of length, giving to the whole the
appearance of organ pipes.
The place for their disposal is the floor, on which, however,
the child has previously spread a mat sufficiently large to accom-
modate himself and the working material, having built up Ms
organ pipes, he pulls them apart, mixes them up and starts afresh,.
repeating this just as often as he gets pleasure from it.
A similar exercise carried out on mats is that of putting
together a series of prisms of chestnut colour, all of the same length
(20 cms.), but having different square sections, ranging from 10 cms.
sides in the largest square, down to 1 cm. in the smallest. The
prisms, from the thickest to the thinnest, are placed one beside the
other in graduated order, in a manner which suggests a staircase.
Finally,a series of cubes, the square end of which decreases from
lOcms. to 1 cm., coloured bright pink., presents objects differing in the
three dimensions, from the largest to the smallest. The largest cube
is placed first on the carpet, then all the rest, one above the other,
thus building up a kind of tower. This is demolished, then re-built^
FORCE AND MUSCULAR
The children take up the blocks with one hand only. The
hand of a child three and a half years old finds it difficult to grasp